Optical networks provide a tremendous capacity advantage. Entities wishing to take advantage of the advantages that optical networks offer, must usually make a decision based on their current needs (which may be modest and predictable) and their future needs (which are typically unpredictable). An entity may decide to acquire a network to meet its short-term needs because of the entity's present financial constraints.
However, this approach carries a risk that the network will be insufficient and may cost more in the long run because the entire network has to be replaced due to inadequacies of the network. Also, any upgrades may require the network to be shut down prior to the upgrade. Such a shut down is costly since no service can be provided, which in turn shuts down a revenue stream. In an industry like telecommunications, a shut down can be extremely costly.
Another approach is to project a long-term need and acquire a network with capabilities to meet the long-term need. This approach also carries inherent risks as well. In the short run, the investment in the network will be wasted to the extent that there will be excess capacity. In the long run, the needs of the entity may change in a different direction and the acquired network will not be able to handle the changed needs efficiently.
Current optical networks typically consist of a collection of point-to-point wavelength division multiplex (WDM) links with optical-electrical-optical (OEO) switches or regeneration sites providing interconnections between links. FIG. 1 is an example of a conventional optical network 100. The optical network 100 includes a collection of OEO nodes (for example, nodes 102, 104, and 106) and regeneration sites (for example, 108).
Not all of the optical traffic flowing into an OEO node is destined for that node. For example, some of the optical traffic flowing from the OEO node 102 into the OEO node 104 may actually be destined for the OEO node 106. However, due to the configuration of the conventional optical network 100, and in particular due to the configuration of the conventional OEO node, all optical signals flowing into the OEO node undergo optical to electrical conversion and all signals flowing out of the OEO node undergo electrical to optical conversion. Thus, the optical signal traffic from the node 102 to the node 106 via the node 104 undergoes optical-electrical-optical conversion at the OEO node 104.
As the amount of express traffic (traffic that is not terminated or regenerated at a node) increases, it becomes cost effective to keep these channels in the optical domain and bypass the OEO switches. This functionality is termed optical bypass.
It is anticipated that the movement to networks with optical bypass will take place gradually by enhancement of existing networks, rather than through builds of complete all-optical networks. In particular, it is expected that bypass capability will only be added to a particular node when the express traffic through that node reaches a capacity level where bypass implementation is cost effective.
It will be very important to carriers to not take down existing traffic terminating at the OEO nodes as the upgrade to optical bypass takes place. Thus, it is very desirable to have a modular upgrade path so that networks OEO nodes and regeneration elements can be upgraded in a hitless fashion in the future.
An approach is desired where the system deployed is extremely flexible so that future demands on the optical networks, not yet foreseen, may be handled with ease. As the capacity demand grows and changes, it is desirable to provide a flexible system that can meet the increased demand and the type of demand changes. It is also desirable to have the capability to recover previously inaccessible capacity and without service disruptions.